While a number of possible approaches have been suggested to permit the substitution of blackplate for tinplate in the manufacture of drawn and ironed unitary can bodies, none has been commercially attractive.
We have developed a technique which utilizes a novel composition as a lubricant for can-making from blackplate without requiring any change in equipment from a conventional tinplate D&I operation. Our composition comprises (1) an acrylic acid/acrylic ester polymer, (2) a wax, and (3) finely-divided molybdenum disulfide. It also desirably employs a temporary cross-linking agent of the type disclosed in Rogers U.S. Pat. No. 3,308,078 to act as a binder for the MoS.sub.2, and an emulsifier/stabilizer.
Combinations of molybdenum disulfide and binders, such as carboxymethylcellulose with amine-functional silanes, have been proposed for metal working. See U.S. Pat. No. 3,843,529 and U.S. Pat. No. 3,881,048, wherein the MoS.sub.2 is also used in combination with graphite. Various other fine abrasives have been proposed--see Montgomery U.S. Pat. No. 2,112,632.
The concept of "binding" a solid lubricant such as MoS.sub.2 to a substrate for metal-working lubrication is discussed in the Oct. 1, 1973 issue of Chemical Engineering, pages 56-66. Various synthetic resins have been proposed, such as celluloses and acrylics, for amenability to curing in air. Others, such as phenolics, epoxies, silicones, and polyimides are heat-cured.
Water-soluble resins such as acrylic acid/acrylic ester resins have also been proposed for drawing and ironing, in combination with waxes and with certain metal oxides. See Derwent Basic Abstract 79838X/43.
The reader may also be interested in U.S. Pat. No. 3,287,264, which employs acrylic polymers, condensation resins, wax, and MoS.sub.2 in an organic solvent, U.S. Pat. No. 3,250,103, which describes petroleum and paraffin waxes used in combination with various polymers for metal working, U.S. Pat. No. 3,478,554 suggesting the use of polyethylene as a lubricant, and Parkinson U.S. Pat. No. 3,873,458 proposing an ammonium aqueous-based lubricant comprising polymers of ethylene and carboxylic acid-containing monomers and molybdenum disulfide. Certain inorganics have also been suggested. But, so far as we are aware, no one has found a composition which can accommodate the demanding conditions of can-making by drawing and ironing.
To be effective and commercially attractive, a lubricant composition must dry quickly and "set" or cure firmly to retain the solid component. If the lubricant is not dry and firm, it will tend to rub off the cup wall or will migrate to the inside of the cup during the cupping operation (tending to inhibit stripping) and/or will abrade off the bottom of the cup onto the conveyor. It should not be immediately water-soluble or susceptible to being washed off by plain water or ironing coolant.
Of all common metal-working processes, such as wire-drawing, deep drawing, and the like, the process of drawing and ironing cans is generally conceded to be the most demanding. In the use of tinplate, the tin tends to act as a solid lubricant; without tin, it has been extremely difficult to make even a few cans without scoring and galling.
Typically, the kinds of problems which can develop with a poor lubricant are excessive scoring and galling of the outside can wall surface, failure to produce smooth, highly polished surfaces, and metal pickup on the dies.